Wire blades

ABSTRACT

Making a wire pack in which a plurality of wires of predetermined length extend between a pair of spaced supports by wrapping turns of wire in a helix around a cylindrical roll while maintaining a constant tension on the wire, placing the supports in position adjacent but spaced from each other and extending axially of the roll and clamping the wire to the supports, and then cutting the wire segments extending between the adjacent supports.

This is a division of application Ser. No. 917,918, filed June 22, 1978now U.S. Pat. No. 4,178,670 issued Dec. 18, 1979.

FIELD OF THE INVENTION

This invention relates to wire blades for cutting hard materials intowafers.

BACKGROUND OF THE INVENTION

It is desirable to be able simultaneously to cut a number of preciselysized wafers from an ingot of silicon, sapphire, quartz, or similar hardmaterial. Such precision cutting, especially of thin wafers, can best beachieved if the blades are exactly spaced and under the same tension;but that is a difficult goal to achieve, especially with wire bladeswhich easily deflect. U.S. Pat. Nos. 3,079,908, 3,168,087, 3,263,670 and3,326,071 disclose cutting machines using multiple rectanglular blades,and in practice wire blades have been used in corresponding commerciallyavailable slicing machines, such as the Model 686 Wafering Machine ofVarian Associates, as disclosed in U.S. Pat. No. 4,092,972 which is hereincorporated by reference.

SUMMARY OF THE INVENTION

It has been discovered that wire blades can be clamped in a blade packat equal tension and with equal spacing between each wire if the pack ismade by winding wire in a helix around a generally cylindrical rollwhile maintaining a constant drag on the wire, clamping the wire wrappedon the roll between two sets of clamps extending axially of the roll,and spaced circumferentially from each other, and then cutting the wireportions between the sets of clamps. In the preferred embodiment, theroll is exteriorly threaded (pitch less than 0.02 in.), the rolltranslates axially a distance equal to its pitch during each rollrotation as the wire is wound onto it, and each set of clamps is mountedin a milled axial slot in the roll periphery.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The drawings show a preferred embodiment of the invention, which is thendescribed. In the drawings:

FIG. 1 is a perspective, somewhat simplified, view of preferred wirepack winding apparatus;

FIG. 2 is a perspective view of the slip clutch and supply spool of thesystem of FIG. 1;

FIG. 3 is a sectional end view of the roll and wire clamp of the systemof FIG. 1;

FIG. 4 is a sectional view taken at 4--4 of FIG. 3; and

FIG. 5 is an enlarged view of a portion of FIG. 4.

Referring now to the drawings, an exteriorly threaded roll 10 is fixedon coaxial threaded shaft 12 which itself is threaded through a pair ofspaced supports 14, 16. An offset crank handle 18 is provided at one endof shaft 12. The helical threads of roll 10 and shaft 12 both have thesame pitch, 1/64 in., so that the roll will translate axially one threadper revolution of shaft 12.

A spool 20 of wire 22 (copper clad wire having a steel core 0.005 l in.diameter and 0.0015 in. thick cladding) is mounted on a shaft 26journaled in support 28 parallel to and about 18 in. from shaft 12. Asmall (1/60 hp.) geared-down electric motor 30 mounted on support 28drives shaft in counterclockwise (as viewed in FIG. 1) at a speed ofabout 1 rpm. Spool 20 itself is freely rotatable relative to shaft 26.An adjustable slip assembly couples shaft 26 and spool 20 providing atorque tending to rotate spool (as shown in FIG. 1) counterclockwise. Asshown in FIG. 2, the clutch assembly comprises, on each side of spool20, a pair of discs 32 and a felt clutch pad 34 between and engaging thefacing surfaces of each pair of discs. The pair of discs 32 andintermediate pad 34 nearest motor 30 are held axially in place by nuts36. A helical spring 38 surrounds the shaft on the other side of spool20 and is forced against the outer one of the other pair of discs 32 byan axially adjustable disc 40 and adjusting nut 42.

Midway between spool 20 and roll 10, a guide pulley 44 is mounted forrotation on a shaft 46, parallel to shafts 12 and 26 and journalled insupport 48. Pulley 44 has a V-shaped groove the top of the base of whichis positioned slightly above a straight line extending from the top ofthe wire wound on spool 20 to the top of roll 10. Thus, wire extendingfrom spool 20 over pulley 44 to roll 10 is deflected slightly upwardly,and positively positioned by guide pulley 44.

Referring more particularly to FIGS. 3 and 4, the exterior surface 50 orroll 10 is threaded, 64 threads per inch, along its entire 6 in. length.Each thread 52 has a 60° included angle and a major diameter of 5.204in. A 1.500 in. wide, 0.500 in. deep at its side edges axial slot 54 ismilled into the outside of roll 10. Mounted in slot 54 are two clampsbases 56, 57, each 1/2 in. wide and about 0.49 in. (as shown in FIGS. 3and 5, the 0.500 in. slot depth less the distance from the exterior ofthe roll to the bottom of wire wound in the threads) high and extendingthe full axial length of roll 10. One end of the slot is closed by aback-up plate 58 which provides a reference permitting the clamp basesto be exactly positioned axially relative to each other. Clamp bases 56,57 are held in place in slot 54 by cap screws 60, one at each end ofeach base, extending from counterbores in the clamps into threaded holesin roll 10.

Turns of wire 22 wrapped around roll 10 in threads 52 lie on the flattop surfaces of clamp bases 56, 57 and are clamped in place by clamptops 62, 63. As shown in FIG. 3., the exact height of the clamps isbelow the level of the thread grooves so that the transition at thesides of slot 54 as the wires pass between the clamping surfaces and theroll threads is as smooth as possible. A flat, thin strip of deformablemetal 64, typically copper, is placed on top of the wire turns on eachclamp base 56, 57, between the wire turns and the flat bottom clampingsurfaces of clamp tops 62, 63.

As shown, clamp tops 62, 63 are each about 1/2 in. wide and 1/2 high,and are about 1 inch shorter than clamp bases so that cap screws 60 areaccessible when the clamp tops are in position on the clamp bases. Capscrews 66, one at each of each clamp to 62, 63, extend through the clamptops into respective threaded holes in clamp bases 56, 57. When thescrews are tightened, the clamp tops are drawn tightly down onto theclamp bases, firmly holding the wires therebetween. The deformable metalstrips 64 assure positive gripping.

In operation, clamp bases 56, 57 are bolted in place in slot 54, andcrank 18 is then turned (counterclockwise as shown in FIG. 1) until thetop of the thread 52 on which winding is to begin lies in a planeperpendicular to the axes of shafts 12 and 46 and passing through theapex of the V-shaped base of pulley 44. Shaft 12 is then locked inplace, and wire from spool 20 is fed from it, over pulley 44, into thealigned thread 52, and into slot 54 between clamp bases 56, 57. The endof the wire is there held by a set screw 70 in the side of clamp base56.

Motor 30 is then actuated, causing shaft 26 to rotate counterclockwiseand, through the adjustable slip clutch assembly, exert acounterclockwise torque on spool 20 and a corresponding drag (typicallyof about one pound on wire 22). Shaft 12 is then unlocked and the wire,with the drag being exerted on it, is then wound on the spool by turningcrank 18 clockwise (as shown in FIG. 1).

When the desired number of wire turns have been wrapped around roll 10,shaft 12 is again locked in place, copper strips 64 are placed over thewire turns on each clamp bar 56, 57, and clamp top 62, 63 are bolted inplace. After the clamp tops have been securely tightened, motor 30 maybe turned off.

The short exposed wire portions between the two sets of clamps (eachincluding a clamp base and top) are then cut, and the cap screws 60holding clamp bases 56, 57 in place in slot 54 are removed.

When the clamps and wire have been removed from roll 10, the result is awire pack including plurality of wires (typically about 250 wires) ofthe same length (about 15 in.) and spaced exactly 1/64 in. from eachother, tightly held by and extending between the sets of clamps. Thewire pack may then be mounted in a cutting machine and the wirestensioned in the usual manner.

OTHER EMBODIMENTS

Metal strip 64 is unnecessary when the copper or other soft cladding ofwire 22 is itself sufficiently deformable to insure the necessarypositive grip between the wire and clamps. Similarly, the roll 10 onwhich the wire 22 is wrapped does not necessarily have to be cylindricalor threaded, especially if close wire spacing is used. If, for example,a wire alignment fixture is provided adjacent clamp bases 56, 57 (e.g.,between or at one side of the clamps) to position the wire as it crossesover the clamp bases, or the clamp bases themselves are slotted foralignment, threads 52 may be omitted and a smooth cylindrical roll used.In any event, the wire 22 may be purchased already charged withabrasive, charged after mounting in the cutting machine in the mannerdisclosed in U.S. Pat. No. 4,092,972, or used in a three-body cuttingprocess as also described in said Patent.

Other embodiments will be within the scope of the following claims.

I claim:
 1. A wire blade pack comprising:a pair of relatively movablespaced supports; and a plurality of wires engaged by and extendingbetween said supports, each of said supports including a pair of opposedclamping surfaces engaging said wires and fixing said wires relative tosaid support with adjacent ones of said wires spaced at regularintervals from each other, the length of each of said wires between saidsupports being the same, and the distance between adjacent ones of saidwires at each of said supports being the same.
 2. The wire blade pack ofclaim 1 wherein each of said supports comprises a clamp base ofgenerally rectangular transverse cross-section, a clamp top, and meansfor drawing said base and top tightly together.
 3. The wire blade packof claim 2 wherein each of said supports includes a step of relativelydeformable material engaging said wires and one of the top and base ofsaid support.
 4. The wire blade pack of claim 2 wherein said top of eachof supports is shorter than the base thereof.